Colorectal Cancer and Disinfection Byproducts in Italy and Spain

S-31B8-3 Background/Aims: Experimental data suggest that disinfection byproducts (DBPs) are colorectal carcinogens but epidemiological evidence is contradictory. To evaluate colorectal cancer risk associated with long-term DBP exposure. Methods: A case-control study was conducted in Italy and Spain. Cases were newly diagnosed and histologically confirmed, aged 20–85 years, and living in the study areas. Controls were matched to cases by age, gender, and area of residence. Study area comprised Barcelona (Spain) and Milan, Pordenone and Udine (Italy). Study subjects were interviewed on potential risk factors of colorectal cancer, residential history and water uses including ingestion, showering, bathing, dishwashing, and swimming in pools. Blood samples were collected to obtain DNA sample. Retrospective data on trihalomethane levels in the study areas have been collected through water companies, and water samples have been collected to measure a range of DBPs. Results: Based on 500 cases and 436 controls in Spain and 400 cases and 363 controls in Italy, the longest residence lasted 35 years on average in Spain and 37 years in Italy. Drinking water at the longest residence was from public water supply among 56% subjects in Spain and 46% in Italy. The rest consumed bottled water or from other sources. Those drinking water from public supplies compared to bottled water had an odds ratio and 95% confidence interval of 1.17 (0.87–1.58) in Spain and 1.18 (0.79, 1.77) in Italy, adjusting for potential confounders. Taking long compared to short showers (above vs. below median) yield an odds ratio of 1.04 (0.80–1.40) in Spain and 1.16 (0.83–1.63) in Italy. Mean trihalomethane levels in Italy were <10 μg/L and ranged from 17.6 to 134 μg/L in Spain. Residential trihalomethane level was associated with an increased colorectal cancer risk for some exposure categories without a clear dose-response. Conclusion: These initial results suggest a weak association between colorectal cancer and DBP exposure.